Background/Hypothesis: The genetic mutation in Friedreich’s Ataxia (FRDA) is a hyper-expansion of the triplet repeat sequence GAA•TTC within the first intron of FXN gene. Normal alleles have 6~34 repeats while FRDA patient alleles have 66~1700 repeats. Although yeast and reporter construct models for GAA•TTC repeat expansion have been reported, studies in FRDA pathogenesis and therapeutic development are limited by the availability of an appropriate human cell model in which to study the mechanism of GAA•TTC triplet repeat expansion in human genome.

 

Methods: Induced pluripotent stem cells (iPSCs) were generated from FRDA patient fibroblasts after transduction with the four transcription factors Oct4, Sox2, Klf4 and c-Myc. These cells were differentiated into neurospheres and neurons, representing a valuable cellular model for FRDA.

 

Results: During the course of these studies, it was observed that during propagation of the FRDA iPSCs, GAA•TTC repeats expand in a manner analogous to the expansion observed in FRDA patient samples, but not in fibroblasts and neurospheres. Importantly, asymptomatic, heterozygous carriers show GAA•TTC triplet repeat expansion on the pathogenic allele, but not the normal allele. The mismatch repair enzyme MSH2, implicated in repeat instability in other triplet repeat diseases, is highly expressed in pluripotent stem cells and occupies FXN intron 1. In addition, shRNA silencing of MSH2 impedes GAA•TTC triplet repeat expansion.

 

Conclusions: GAA•TTC triplet repeat expansion is recapitulated in FRDA iPSCs but not fibroblasts or neurospheres. The mismatch repair enzyme MSH2 is involved in the GAA•TTC triplet repeat expansion.

 

Jintang Du博士简历

1997-2001   B.S. in Chemistry in Lanzhou University / Prof. Yulin Li

2001-2006   PhD in Organic Chemistry in Tsinghua University/Prof.Yanmei Li

2007-2009   Postdoctoral research in Cornell University / Dr. Hening Lin

Since2010   the Scripps Research Institute for Research, Prof. Joel M. Gottesfeld

1.      Develop specific HDAC inhibitors to treat human neurodegenerative diseases.

2. Use patient-derived induced pluripotent stem (iPS) cell model to study human neurodegenerative diseases and identify the molecular mechanisms.

3. Identify specific histone deacetylases (HDACs) involved in human neurodegenerative diseases using HDAC siRNA knockdown and HDAC inhibitors.